The former prime minister of Kyrgyzstan was shown late Sunday with an early lead in the Central Asian nation's first presidential election since the deadly 2010 uprising that toppled former President Kurmanbek Bakiyev.

Kyrgyz election officials issued the partial, unofficial tally showing Almazbek Atambayev leading a field of 16 candidates that included the ousted president's former Emergency Minister, Kamchibek Tashiyev, and former Speaker of Parliament Adakhan Madumarov. Both Tashiyev and Madumarov are from the south, while the former prime minister hails from the north of the ethnically divided nation.

Interim President Roza Otunbayeva, who has led the country for the past year, did not run.

As the polls closed, Madumarov appeared ready to challenge vote returns, complaining to journalists that tens of thousands of people were not permitted to register. Other challengers were reporting allegations of repeat voting and ballot box stuffing.

International observers did not immediately comment on the allegations.

Voting Sunday was reported brisk in the capital, Bishkek, and the Kyrgyz Central Election Commission later said more than 60 percent of the electorate cast ballots.

Kyrgyzstan hosts both U.S. and Russian military bases and is a crucial hub for NATO operations in Afghanistan.

On the campaign trail, the top three candidates have said they would respect the U.S. base lease, which expires in 2014.

Less controversial is a Russian base on the other side of Bishkek, a legacy of Soviet days.

Geography divides the mountainous ex-Soviet country between north and south, and ethnicity further splits the population of 5.5 million.

Last year, in Kyrgyz cities bordering Uzbekistan, rioting broke out between ethnic Kyrgyz and ethnic Uzbeks. When the fight was over, about 500 people were dead, thousands were wounded and thousands of houses were in ruins.

Earlier this month, Atambayev traveled to Moscow where he met with Russian Prime Minister Vladimir Putin. He is the only candidate to win such an audience. Kremlin approval is key in a country where one-quarter of adult males work in Russia.